President Barack Obama, with the President of South Korea Park Geun-hye, responds to a question during a joint press conference in the East Room of the White House on May 7, 2013. (EPA/SHAWN THEW)

President Barack Obama on Tuesday said the U.S. has moral and national security obligations to respond to Syria’s bloodshed, but he continued to urge caution about what he said was “perceived” use of chemical weapons in the Middle Eastern country.

“We have evidence that there has been the use of chemical weapons, but I don’t make decisions based on ‘perceived,’” evidence, Mr. Obama said as a press conference at the White House with South Korean President Park Geun-hye. He said his decision on how to respond to the Syrian conflict must be based on “hard-headed analysis.”

Mr. Obama has been under pressure from international allies, human rights groups and others about how the U.S. will respond to the use of the banned and deadly nerve agent Sarin in Syria. It’s unclear who is responsible for the use of chemical weapons in the country — rebels or those loyal to Syrian President Bashar al-Assad. Mr. Obama has previously said the use of chemical weapons would cross a red line, prompting further action.

“I think that we have both a moral obligation and a national security interest in, A, ending the slaughter in Syria but, B, also ensuring that we’ve got a stable Syria that is representative of all the Syrian people and is not creating chaos for its neighbors,” Mr. Obama said.

Republican lawmakers and deficit hawks have urged the president to take more action against the Assad regime, saying they are concerned that if he doesn’t back up his words with action other authoritarian regimes won’t take his threats seriously. “There have been several instances during the course of my presidency where I said I was going to do something, and it ended up getting done,” Mr. Obama said.

“In the end, whether it’s bin Laden or Gadhafi, if we say we’re taking a position, I would think at this point, the international community has a pretty good sense that we typically follow through on our commitments,” Mr. Obama added. He was referencing al Qaeda’s Osama bin Laden, who was killed by U.S. forces in May 2011, and Moammar Gadhafi, the Libyan leader who was killed in October 2011 during an uprising of anti-Gadhafi forces.

The Obama administration has said it’s considering arming the rebels to help fend off Mr. Assad’s government and end a war that has killed more than 70,000 and displaced millions across the border into country’s such as Jordan and Turkey. Mr. Obama defended his administration’s response so far.

“I think there’d be severe costs in doing nothing. That’s why we’re not doing nothing,” Mr. Obama said. The U.S. has provided Syria with humanitarian aid and tried to rally the international community to pressure Mr. Assad to go.

Ms. Park spoke to the issue of North Korea, saying the U.S. and South Korea are closely aligned in trying to get the country to end its provocative behavior. While tension has eased in recent weeks, Ms. Park had a tough first few months in office with Pyongyang making near-daily threats of war. Mr. Obama praised her “calm and steady resolve” in the face of the threats.

Ms. Park’s visit to the U.S. was her first foreign trip since becoming president. While she and Mr. Obama talked extensively about North Korea, the two leaders also discussed ways to deepen economic ties. Ms. Park said she asked the president to help make sure Congress passes legislation to ensure Koreans can get high-skilled work visas to work in the U.S.

She is scheduled to address Congress on Wednesday.

Separately, Mr. Obama responded to concerns about sexual assaults in the military. He said he has no tolerance for sexual assault and expects consequences. “If we find out somebody’s engaging in this stuff, they got to be held accountable, prosecuted, stripped of their positions, court-martialed, fired, dishonorably discharged — period. It’s not acceptable,” Mr. Obama said.

The remark were prompted by a new Pentagon report showing the number of military sexual assaults reported in an anonymous survey jumped sharply to 26,000 last year.

The report followed a Pentagon announcement Monday evening that it removed the Air Force officer in charge of the services sexual assault prevention efforts from his post after he was charged by police with sexual battery.

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